The effects of single oral doses of 3,3',4,4', 5,5'-; 2,2', 4,4', 5,5'-; and 2,2', 3,3', 5,5-hexachlorobiphenyls on lipid metabolism in the rat are being studied relative to levels of activity of fatty acid-CoA ligase, glycerol-3-phosphate acyl transferase, diacylglycerol acyl transferase, diacyl glycerol choline phosphotransferase, lysophosphatidic acid acyl transferase and phosphatidic acid phoshohydrolase. In addition, the effects of the above PCBs on microsomal drug-metabolizing enzymes and on the electrophoretic properties of cytochrome P-448/450 are being examined. The general goal of these studies is to relate PCB structue to some of its mechanisms of action.